Wireless communication systems typically use an RF power amplifier to carry out the transmission. These power amplifiers are typically linear over only a certain range of input power. Beyond that range, the RF power amplifier will gradually saturate. As link conditions change, a power control loop may adjust the output power of the transmitter to maintain a desired quality of service.
Link conditions can change because of location, channel fade, rain fade, transceiver characteristics such as aging, temperature, condition of the hardware, or myriad other reasons.
It may be useful to detect and/or avoid operating the RF power amplifier in a non-linear region. Avoidance may be important, for example, in certain kinds of modulation schemes which have non-constant envelopes. Saturation and non-linearity can distort these signals and/or cause spectral regrowth.
Systems of this type have estimated the onset of nonlinearity using various techniques. Current sensing techniques, correlation methods, and subsampling techniques may require specialized hardware at the amplifier. Other techniques may estimate nonlinearity in a power amplifier that communicates with a satellite modem. This system may add to the cost of the unit. US Patent Publication number 2002/405781 describes a system that requires knowledge of the transmitted data sequence and models the transmission amplifier based thereon.
It is possible to measure the transmitted power at a transmitted output, e.g., the output of the outdoor satellite unit. In such a system, the onset of saturation would be detected as the power levels increase. Such a system would require additional hardware at the outdoor unit. It could also require hardware in the data channel in order to transmit the telemetry back to the modulator.
The onset of saturation can be met with remedial measures such as reducing the data rate or changing to a more robust coding or modulation scheme.